A Direct Approach for the Frequency-Adaptive Feedforward Cancellation of Harmonic Disturbances

This paper is concerned with the robust rejection of harmonic disturbances with unknown frequency and amplitude affecting uncertain linear system. The developed control scheme combines the properties of adaptive feedforward cancellation (AFC) techniques with the phase and frequency detection capabilities provided by a nonlinear frequency estimation algorithm. Under mild assumptions on the nominal model of the system to be controlled, the proposed scheme is proven to achieve the complete rejection of harmonic disturbances at the input or at the output of the system. A detailed stability analysis based on averaging provides useful informations on the effect of the tuning parameters over the convergence of the estimator. The effectiveness of the proposed approach is demonstrated by a two-time scale averaging analysis.